SHARP stands for the Safety Helmet Assesment and Rating Programme and is a scheme designed to deliver clear and easy to understand information about the safety of your helmet.
Each model studied by SHARP is tested 32 times across 7 helmets of varying sizes and are assessed on their ability to minimise the likelihood of brain injury. These impact tests are done at three different speeds and results gathered from an accelerometer inside the helmet determines the amount of energy absorption offered by the helmet.
The star ratings that are offered by SHARP are based off these energy absorption readings when compared against real life crash data so offer real world data.
To ensure independence of the scheme all the helmets tested are purchased from retailers and not acquired from manufacturers themselves.
Thinking of getting a new helmet or wondering what score yours got? [Mine got 5!]
Have a look at http://sharp.direct.gov.uk/home.